1. Field of the Invention
This invention relates to the controlled release into the atmosphere of active substances such as air fresheners, fragrances or pheromones from a solid carrier or matrix. More particularly, this invention relates to matrices which are solids at room and ambient temperatures which are useful for controlled release of such active substances. The matrices have a glass transition temperature such that various active substances can be incorporated by melting or softening the matrix composition and mixing the active substance into the softened composition.
2. Description of the Prior Art
Matrices have hithertofore been used as reservoirs for containing and releasing active substances such as fragrances or pheromones. Representative of this prior art is U.S. Pat. No.4,703,070 to Locko, et al, issued Oct. 27, 1987. Hithertofore, as described, for example, in that patent, the active substances were incorporated into resinous or elastomeric materials which were subsequently cured or cross-linked. It has not been feasible to incorporate many types of active substances into such systems in which the cure is not complete at the time the substance is incorporated into the composition, because the active substance may be deleteriously affected by either the vulcanizing temperatures which in many cases are required to cure the polymer, by the ingredients of the prepolymer, which may contain reactive components that react with the active substance, or the curing agent which may interact with some active substances. In the case of the latter interactions the active substance inhibits the curing agent in some cases, while the curing agent affects the characteristics of the active substance in other cases.
An objective of this invention is to provide materials for matrices that enable the migration therethrough of a variety of active substances and which can be melted or softened to the extent that such substances can be admixed therein at relatively low temperatures, ie., about 45.degree. C. to 160.degree. C., which temperature in each case is low enough to avoid thermal damage to the active substance. The matrices of the present invention are thermoplastic materials which do not require the presence of curing agents, prepolymers, or catalysts. By elimination of the need of using such ingredients which might themselves impair the efficacy, odor or other characteristics of the active substance which is to be released, a number of problems encountered with the prior art thus are eliminated.